The goal of this project is to investigate effects of halothane on liver cell structure in rats that have been subjected to one of two pretreatments: (1) pretreatment with phenobarbital prior to halothane administered during hypoxia or (2) pretreatment with Aroclor 1254, a polychlorinated biphenyl mixture, known to induce an altered form of cytochrome P450 (cytochrome P448), a microsomal enzyme responsible for the metabolism of halothane. The project will evaluate the effects of the pretreatments with and without halothane on: (1) liver structure by electron microscopy, (2) the concentration of cytochrome P450 or cytochrome P448 (as an index of microsomal enzyme induction) and (3) plasma fluoride concentration (as an index of a shift in halothane biotransformation from an oxidative route to a reductive route). Similar studies will investigate the response of liver morphology to other volatile anesthetics following the pretreatments. This study will: (1) document the suitability of these preparations as models for the study of hepatic injury precipitated by halothane and (2) determine if the hepatic cellular response is specific for halothane following such pretreatment. Hepatic morphologic changes following the various treatments will be assessed quantitatively using morphometric techniques. Data thus developed by this project will provide a basis for comparing the cellular morphologic effects of a variety of anesthetics.